Piston ring



April 8, 1952 R. H. co| v|N 2,591,920

PIsToN RING Filed Nov. 24, 194'? E Z6 f8 52 ff ?2/ E Ew 27 fig.

IN VEN TOR.

ATTYS.

Patented Apr. 8, 1952 PISTON RING Robert H. Colvin, Delavan, Wis., assignor to Burd Piston Ring Co., Rockford, Ill., a corporation of Illinois Application November 24, 1947, Serial No. 787,64]

' 9 Claims. (Cl. 309-44) This invention relates to piston rings and more particularly to split piston rings of the type in which the twisting or torsion of the ring is controlled in a predetermined manner when the latter is compressed to t in a cylinder bore.

In general, split piston rings are formed from out-of-round castings or the like. This out-ofround shape of the blank ring in the free or uncompressed condition is required so that when the ring is compressed in an operating condition in a cylinder bore, pressure will be exerted by the ring against the cylinder walls. Although this ring pressure is frequently referred to as being uniformly distributed about Vits periphery when in the compressed state, it is to be understood that this is not exactly true. The ring pressure actually varies as much as 11/2 to 1 or 2 to 1 and even more at different points about the ring periphery. Due to the many 'variables in piston lring manufacturing it is practically impossible to obtain rings that willhave a perfectly uniform pressure distribution. Accordingly, manufacturers design the rings for a predetermined pressure distribution pattern which through experience has been found to be satisfactory. This pressure pattern varies from manufacturer to manufacturer. Thus, some manufacturers use a pressure distribution pattern that is cardioid shaped, others use a pressure distribution pattern that is pear shaped, and others use still different shaped pressure patterns.

The aforegoing is best understood when it is considered that the ring is normally of an outof-round shape vin the unstressed condition, and in compressing thering to a true circle to t the cylinder bore, portions of the ring are not stressed exactly the same. For example, when an elongated bar having a square section such asa steel bar is bent into a circle, the inside edge of the section will tend to become thicker due to compression and the outside edge o f the section will become smaller due to stretching. When materials such ascast iron and similar materials having relatively non-compressible and nonelastic characteristics, such Yas are .used in Vpiston rings, are used under the above conditions, the formed section is distorted by twisting. Thus, no matter how flat and parallel the top and bottom sides of a piston ring, formed from maaterial having a generally rectangular shape, are when in the free state, when the ring is compressed to the cylinder diameter, they are no longerA flat and parallel.

In finishing piston rings, that is, in fashioning the rings to the correct outside diameter. a group of ring blanks are compressed to the approximate outside diameter and are then placed in side by side relation and compressed as by an arbor. The rings are then ground, polished, or honed and the like to the correct diameter. It is readily apparent that when this operation is completed that the rings will have been compressed to diameter and flattened by the vendwise pressure. Thus, the rings in the nished form are inherently under twisting or torsional forces as described above. l

Because of this twisting, theouter peripheral surface is not truly at right angles to the sides of the ring. Such a ring when it is compressed to diameter in a ring groove in a piston having side clearances and reciprocable in a cylinder bore will not present a ring surface that is a true cylindrical surface. At some portions around the ring the top edge thereof willbear on the cylinder walls, at other points the bottom edge will bear on the cylinder walls, and in some cases an intermediate portion will bear on the cylinder walls. In some instances it is desirable to form the ring so that only one edge for example the bottom edge of the ring will engage the walls of the cylinder, particularly in the case where the ring is used for the purpose of sealing compression and controlling oil usage. In such cases, however, it is desired that this edge engage the cylinder walls at all points around the entire periphery of the ring. Where there is torsion and twisting in the ring when it is compressed `as above described vthis is not always possible.

An object of my invention is the provision of a piston ring wherein the twisting and torsion of the ring is `controlled in a predetermined manner so that a predetermined surface on the ring, throughout its periphery, is brought to bear against the cylinder walls.

Another object of the invention is to provide Aa piston ring of the above character in which Fig. 4 is a sectional view of the ring taken along the line 4-4 of Fig. 2;

Fig. 5 is a plan view of another piston ring embodying a modification of the invention;

Fig. 6 is a sectional view taken through `line 6--6 of Fig. 5;

Fig. 7 is an elevational view of another piston ring embodying another modification of the invention, and

Fig. 8 is a view taken substantially along the line 8-8 of Fig. 7.

Referring now to the drawings, the invention is shown embodied in a piston ring II of the type adapted for use with a conventional piston I2 arranged to reciprocate in a cylinder bore I3 of an engine, compressor or the like. In general,

the ring is formed from an out-of-round annular member having a shape such as that shown in Figs. 2, 5 and 7. Preferably, it has a generally rectangular shaped cross-section and has a gap Il formed at one position along the periphery to provide opposed faces I6 and I'I on the ring. The length of the gap I4 is such that the ring I I can be compressed to t in the cylinder bore I3.

The invention is concerned with a ring construction Which controls the elastic deformation of the ring in a predetermined manner in the compressed state so that a desired peripheral surface I8 of the ring is positively brought to bear on the cylinder walls I9 and the pressure about the periphery of the ring at the point of contact with the cylinder bore is distributed in accordance with a predetermined pressure distribution pattern. For this purpose the ring is formed with an unbalanced cross-section that varies in a prescribed manner around the periphery of the ring I I. As shown in the embodiment in Fig. 2 this is accomplished by forming a bevel 2| on one inside edge of the ring II. The dimensions of the bevel 2| vary for each particular cross-section along the periphery of the ring as shown by the sectional views in Fig. 3. The dimensions of the bevel are such that there is proportionally more bevel at the points of least bend of the ring when it is compressed to diameter. The amonut of bevel for any section or portion of the ring is inversely proportional to the amount of bend that the particular section will undergo in compressing it to cylinder bore diameter and is directly proportional to the amount of twist desired in the ring section.

The aforegoing can best be seen by referring to Figs. 2, 3 and 4. As previously pointed out the piston ring is made from an annular out-ofround blank of generally rectangular cross-section, the manufacture and design of which is carefully controlled in order to assure that the pressure around the ring when it is restrained in the cylinder bore is distributed in accordance with a predetermined pattern. When the ring is restrained in the bore, the internal stresses in the ring produce an elastic deformation of the ring such that the sides 22 and 23 of the piston ring I I are no longer exactly parallel and the peripheral face 24 is not an exact cylindrical surface so does not have full contact surface with the walls I9 of the cylinder I3. The twist normally varies throughout the periphery of the ring. Thus, the section 180 degrees from a mid-point between the end faces I6 and II, due to higher internal stresses, is usually deformed or twisted the most while the portions adjacent the respective faces I6 and are twisted least because of the proportionately small internal stresses in the ring at this portion of the ring.

It is difficult, if not impossible, to determine by mathematics alone the amount of bevel that should be formed on the ring II for any crosssection. Although it is theoretically true that when a ring is formed from an annular member having a generally rectangular cross-sectional shape in the free state, any cross-section thereof should be symmetrical when the ring is compressed, tests show that this is not true and that deformation apparently does not follow a true mathematical formula since the respective crosssections are not symmetrical on either side of a transaxial plane passing through the center of the ring. This may be due to non-uniformity o1' variations of material or imperfections in manufacturing at, various points about the ring. Because of these discrepancies in the manufacture of a ring it is difficult to develop accurate mathematical formulas by which the amount of bevel 2| for any given section can be readily determined. As a consequence, I have found it neces- .ary as a practical matter to determine the amount of bevel required to obtain the proper twist for any given group of ring sizes by experiment, that is, by tting a sample ring II in a bore of predetermined dimensions and using bluing to determine the fit. Thus, for the nished ring, size 4 inches by E inches, shown in Fig. 2, which is by way of illustration only, I have found that the bevel for the section A-A taken adjacent the face I8 should be a .090 inch by 45 degrees bevel, which means that the chamfer commences on the top surface 23, .090 inch from an inner edge 20 measured along an extension of the top surface 23 and commences on the inner edge 20, .090 inch from the top surface 23 measured along an extension of the inner edge 20. At section B-B on a radius approximately 45 degrees from the face I6, the dimensions of the bevel should be approximately .070 inch by 45 degrees. At section C-C taken on a radius approximately degrees from 'the face I6 the dimensions of the bevel should be .055 inch by 45 degrees. At section D-D taken on a radius approximately degrees from the face I6 the dimensions of the bevel 2| should measure .045 inch by 45 degrees. At section E-E on a radius approximately degrees from the face I8 the dimensions of the bevel should be .040 inch by 45 degrees. Due to the symmetry of the ring shown in Fig. 2 the cross-sections on the right hand side of the ring as shown in Fig. 2 are the same as the corresponding cross-sections for the left hand side of the ring. Thus, it is seen that the dimensions of the bevel 2| from faces I6 and I'I get smaller as the position approximately 180 degrees away is approached. It is to be understood that the bevel 2| can be formed during the casting of the annular blank from which the ring II is formed or can be machined on a pre-cast ring. In casting the bevel 2|, the dimensions of the bevel on the original casting are somewhat larger than indicated above for the finished ring to allow for machining the casting. The allowance for machining in any case will depend on the practice of each individual manufacturer.

Although I have illustrated my invention by employing a non-uniform bevel 2| along one edge of the ring |I it is to be understood that the unbalancing of any section can be effected by notching, grooving or the like. In Figs. 5 and 6 there is shown an embodiment of the invention in which a plurality of annularly spaced stepped MMIV 1?'5 notches 26'iare 'formedfalong `the inner edge of thezringv I I, serving the samepurpose as'the'bevel 2 I ,i.-e., to .unbalance/any :given 'section o'fthezring II. .It is to `be understoodJthatalthough'l have other embodiment of the invention. Inthis rcon- `the ring vII to providean unbalanced cross-section. The dimensions of the groove 21 vary at different cross-sections of the ring in accordance with the foregoing principles. The groove, however, is located at one side of the centerline of;

the section as shown in Fig. 8 so as to obtain an unbalanced cross-section.

tion fof .greatest Iun'balance `lbeing :disposed 'adiacent "thesffacea l 4. A Y'one-piece .ring :comprising v:asplit1annu- "lar member "having fspaced Vopposed :gap "faces,

'the material-fformingfsaid ring :being lunbalanced with` respect to 'the transaxial plane passing mid- ."s'tructionlagroove 2.1 is formed on the interior of n l-way lbetween' the'faxial extremities@ of ythe ming Hto form a 'continuous @unbalanced fcrossfse'ction that varies progressively vabout the ring, the cross section of le'ast"funbalance being disposed at a position 180 degrees from a centerline between said faces and the crosssection of greatest unfbalance .being Adisposed adjacent 'the faces.

The ring construction hereinbefore described irs advantageous in that it provides for a positive resilient seal between the ring I I and the piston I2, thereby assuring a finer degree of control, relative to pumping of oil, than heretofore possible. The dimensions of the groove 28 on the piston I2 are of necessity somewhat larger than the thickness of the ring II in order tof permit assembly. Due to the controlled twisting of the ring II as herein described an upper edge 29 of the ring, about its periphery engagesv the upper wall of the groove 28 as seen in Fig.

wall of the groove. Because of the pre-conf trolled twisting of the ring positive engagement of the walls of the groove and the edges of the ring is assured. This positive engagement bei` tween the ring and the walls of the piston groove results in a construction that controls the pumping of oil to a finer degree than in prior constructions.

I claim: l

1. A one-piece piston ring comprising a split annular member having spaced opposed gap faces and a variable cross section unbalanced with respect to the transaxial plane passing midway between the axial extremities of the ring at pre selected positions around the ring, the cross sections at positions approaching the faces having the greatest unbalance and the cross sectionsft positions approaching a position 180 degrees from a centerline between said faces having the least unbalance to produce a controlled twist at selected positions of the ring when the latter is compressed.

2. A one-piece ring comprising a split annular member having spaced opposed gap faces, said ring having portions extending along the ring" of unbalanced cross section unbalanced with re? spect to the transaxial plane passing midwaybetween the axial extremities of the ring, the cross sectional Yunbalance varying about the ring,the cross section of least unbalance being disposed at a position 180 degrees from a centerlineflfbe'- tween said faces and the cross section of greatest unbalance being disposed adjacent the faceslg,y

3. A one-piece ring comprising a split annular member having spaced opposed gap faces, said ring having annularly spaced portions of unbalanced cross section unbalanced with respect to the transaxial plane passing midway between the axialextremities of the ring, the cross sectional unbalance of the portions varying about the ring, the cross section of least unbalance being disposed at a position 180 degrees from a centerline between said faces and the cross sec- 5. A one-piece piston ring :comprising ka split annular member having opposed faces and a generally rectangular shaped cross section, said cross section at preselected positions about the annular member having a pre-dimensioned area removed therefrom at one side of the transaxial plane passing midway between the axial extremities of the ring to form a cross section unbalanced with respect to said transaxial plane, the

' dimensions of the removed area varying in a predetermined manner around the annular member from a maximum adjacent said opposed faces to a minimum adjacent a position substantially degrees therefrom.

' 6. A one-piece piston ring adapted to have a predetermined surface in engagement with a wall of a cylinder comprising al split annular member adapted to be compressedto t in said cylinder and having opposed faces,v said annular member having a predetermined cross-section unbalanced with respect to the transaxial plane passing midway between the axial extremities of the ring, said unbalanced cross section varying at selected points about the annular member in its uncompressed position, the unbalance of said unbalanced cross vsections being greatest as the selected point approaches'fthe faces and least as the selected point approaches a position 180 degrees from a centerline between the faces, to effect a controlled twist v'of the ring in the compressed state whereby said predetermined surface of the ring engages-the cylinder Walls.

7. A onepiece split piston ring, comprising an annular member having a portion removed on the periphery thereof to form opposed faces, said annular member having-.a generally rectangular shaped cross section and having a pre-dimensioned bevel formed along one edge disposed to one side of the transaxialgplane passing midway between the axial extremities of the ring to form an unbalanced cross-section, the dimensions oi said bevel decreasing arfund said annular member from amaximum Vadjacent said faces to a minimum adjacent a point substantially 180 degrees therefrom to produce a preselected twist in the ring when compressed to operating position.

8. A one-piece piston ring, comprising a split annular member having opposed faces and a generally rectangular shaped cross section, said annular member having afpre-dimensioned annular groove formed on one surface thereof and disposed at one side of the transaxial plane passing midway between the axial extremities of the ring, the dimensionsjof said groove decreasing in a predeterminedmanner around said annular member from a position adjacent said faces to a position 180 degrees from a centerline between said faces.

9. A one-piece split "piston ring, comprising an annular member having opposed faces and a portion removed to provide spaced opposed faces and having a generally rectangular shaped cross section, said member having -annularly spaced grooves formed along one surface and disposed at one side of the transaxial plane passing midway between the axial extremities of the ring, the dimensions of said grooves decreasing in a predetermined manner along the periphery of the ring from a maximum adjacent said faces to a minimum at a position substantially 180 degrees from a centerline between said faces. ROBERT H. COLVIN.

REFERENCES CITED The following references are of record in the le of this patent:

Number "8 UNITED STATES PATENTS Name Date Petter July 27, 1909 Bryant Apr. 16, 1918 Hinckley Apr. 19, 1921 Norman May 24, 1921 Kistner Oct. 11, 1921 Stoiers May 30, 1922 Wenzl Apr. 3, 1923 Booker Aug. 31, 1926 Farmer Aug. 30, 1927 Madsen July 14, 1936 

